: I am putting a washing machine in my basement. It will need to pump up about 6 feet (the pump can handle it) and then into the stack via an old drum trap.

: I assume that the old drum trap (that accommodated the old washing machine) should go.

: Can I discharge the washing machine discharge directly into the stack, or should I put in a P-Trap and also an in-line vent to make sure it doesn't siphon (as the connection between the washer and the piping will be tight)?

Sal,You will need a 2" p-trap, vented either normally or with an in-line vent to prevent siphoning.

Where the hose goes into the drain, should allow for air to move past, not air tight.

They even make hose to standpipe connecters with small air holes built in.